An adapter, also called as a power adapter, is configured to charge a device to be charged (such as a terminal). Nowadays, the adapter on the market typically charges the device to be charged (such as the terminal) in a constant voltage mode. Since a battery in the device to be charged is typically a lithium battery, it is easy to cause lithium precipitation when the device to be charged is charged in the constant voltage made, thus shortening service lifespan of the battery.